feat: remove the licence pages, routes and exceptions

[blaipr]

Follows ctrliq/ascender#1005, which takes the subscription surface out of the platform. The client held three pieces of it, and each now describes something the API does not do.

Config

Six properties read fields that /api/v2/config/ no longer returns:

• is_valid_license wanted valid_key and instance_count, is_trial_license wanted trial, is_enterprise_license wanted license_type == 'enterprise', and features read a features dict. None of those keys are in the payload any more.
• is_ascender_license compared license_type against 'open', which is the only value there is, so it is a property that always returns True.
• is_aws_license read ami-id and instance-id, metadata a Tower AMI put in the licence blob.

Leaving them in place is worse than removing them: a caller asking is_valid_license gets a quiet False rather than an error saying the question no longer applies.

Routes

ConfigAttach posted to config/attach/ and the Subscriptions page posted to config/subscriptions/. config/subscriptions goes with #1005, and config/attach has never been served by ctrliq/ascender, so that page could only ever produce a 404.

Response sniffing

page.py searched every 400 and 403 body for eleven licence phrases, among them Invalid license, License has expired and Missing 'eula_accepted' property, to decide whether to raise LicenseInvalid or LicenseExceeded instead of Forbidden or BadRequest. The platform does not emit any of those phrases now, so every response already took the else branch. The sniffing goes, and the two exception classes with it.

Checks

ruff format --check and ruff check ascenderkit pass, ty check ascenderkit passes, and the unit suite is green at 375 passed, 1 skipped.

[ciq-it-service-account]

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